This invention relates to a liquid crystal light valve and, more particularly, to a light-addressed liquid crystal light valve.
Liquid crystal light valve (LCLV) is an optical switching element used for light projection display, optical data processing, etc. An article entitled "Application of the Liquid Crystal Light Valve to Real-Time Optical Data Processing" by W. P. Bleha et al., in "Optical Engineering", vol. 17, No. 4, July-August, 1978, pp. 371-384 discloses a light-addressed LCLV wherein the device is embodied by sandwiching a film structure of a cadmium sulfide (CdS) photoconductor film, a cadmium telluride (CdTe) light-absorbing film, a multilayered reflection film and a liquid crystal between transparent conductor films formed on a pair of transparent substrates respectively. When a predetermined ac voltage is applied between the transparent conductive films, the liquid crystal is impressed with a partial voltage divided by equivalent capacitors of liquid crystal, multilayered reflection film, CdTe film, and CdS film. When signal light comes in from the transparent substrate on the side of the CdS film, the resistance of the illuminated portion of the CdS film becomes lowered to thereby increase the partial voltage applied to the liquid crystal. The reflection of the projection light incident to the substrate on the side of liquid crystal is varied by controlling the molecular alignment of liquid crystal with the changes in applied voltage.
The foregoing prior art LCLV has at least two problems.
One problem is the difficulty in obtaining a sufficient display contrast at a high level. As mentioned above, the partial voltage applied to the liquid crystal is divided by equivalent capacitors of the multilayered reflection films and so on. Therefore, even if the capacity of CdS film is varied extensively, the voltage applied on a capacitor of the liquid crystal would not change proportionally. As the variation in partial voltage is small, a display contrast cannot be set beyond 5-8.
Another problem is the difficulty in manufacture which also requires time consuming process. To increase the variation of the divided partial voltage, the thickness of CdS film must be made sufficiently thick. However, as will be discussed in more detail hereinafter, it is not easy to form a thick CdS film.